JPS6320907B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a titanium alloy plate. [Conventional technology and its problems] Conventionally, when manufacturing an α+β type titanium alloy plate,
Wide, large slabs made by forging or blooming ingots are used, and when manufacturing these slabs, processing is performed in the β region where deformation resistance is low. Titanium alloy plates obtained by further hot rolling such slabs generally have problems such as extremely poor structural uniformity and mechanical properties (particularly elongation), and are prone to cracking on the surface. There is. The present invention was devised in view of these conventional problems, and aims to provide a method for producing a titanium alloy plate with a uniform structure, excellent mechanical properties such as elongation, and no surface cracks. be. [Structure of the Invention] In the α+β type titanium alloy plate manufacturing process, a slab is made from an ingot by forging or blooming rolling, and this slab is further hot rolled. The reason for the deterioration of uniformity and mechanical properties is that as mentioned above, slabs manufactured in the β region are slowly cooled to a temperature near the βα+β transformation point during the manufacturing stage, which causes the deterioration of the former β grain boundaries. This is because coarse grain boundary α crystals precipitate in a network shape, and a part of them continues to remain without disappearing even after hot rolling and subsequent heat treatment. Conventionally, a method of controlling the processing conditions at the slab manufacturing stage by focusing on the material and structure of the slab has not been adopted, but the present inventors and others As a result of examining the relationship between the microstructure and material properties, we found that mechanical properties such as uniformity and elongation of the structure after hot rolling were significantly improved by subjecting the ingot to strong working at temperatures in the α+β2 phase region during the slab manufacturing stage. I found out that it can be done. In other words, in order to eliminate the network-like coarse grain boundary α crystals that precipitate during the slab manufacturing stage, it is necessary to perform recrystallization accompanied by diffusion. It has been found that energy is accumulated and this strain energy promotes recrystallization during the subsequent reheating process during hot rolling, thereby making the structure uniform. Therefore, the present invention provides α
A +β type titanium alloy ingot is forged or rolled at a total reduction rate of 30% or more at a temperature in the α+β2 phase region to form a slab, and this slab is reheated and then hot rolled. Further, according to further studies by the present inventors, hot rolling is carried out under processing conditions of strong reduction at a temperature in the α+β2 phase region, and furthermore, in the slab manufacturing process before such hot rolling, the α+β2 phase region as described above is produced. It has been found that a more uniform structure can be obtained after heat treatment of a hot-rolled plate by performing intense working at a temperature of . That is, this can be done using α as described above.
A slab that has been subjected to heavy working in the +β2 phase region and has accumulated strain energy is recrystallized by being heated to a temperature in the α+β2 phase region where network-like coarse grain boundary α crystals do not precipitate. After the structure is homogenized, strain energy is accumulated by hot rolling at a temperature in the α+β2 phase region, and this strain energy promotes recrystallization in the next heat treatment process. This is due to the organization becoming more uniform. For this reason, in the second invention of the present application, an α+β type titanium alloy ingot is prepared at a total reduction rate of 30 at a temperature in the α+β2 phase region.
% or more to form a slab by forging or rolling, and after reheating the slab to a temperature in the α + β 2 phase region,
Hot rolling is performed at a total reduction rate of 30% or more. The hot workability of α+β type titanium alloys decreases at temperatures in the α+β2 phase region. Therefore, when applying heavy working in the α+β temperature range, if a slab in which network-like grain boundary coarse α crystals remain is used, this net There is a risk that many hexagonal surface cracks may occur starting from the work-like grain boundary coarse α crystals, but in the above invention, hot rolling is performed using a slab in which the network-like grain boundary coarse α crystals have disappeared. It is possible to prevent surface cracking and to produce a hot-rolled plate with excellent surface properties. The manufacturing conditions of the present invention will be specifically explained below. In the present invention, first, α+β type titanium alloy ingot is
The total reduction is 30% or more by heating to a temperature above the transformation point -200℃ and below the β transformation point +100℃, and then continuously forging or blooming at a temperature in the α+β2 phase region without forcibly cooling in the middle. It is then processed to form a slab of specified dimensions. A batch furnace or a continuous furnace is used to heat the titanium alloy ingot. The reason why the heating temperature was limited as described above is as follows. That is, at a heating temperature below the β transformation point -200°C, the hot workability of the α+β type titanium alloy is significantly reduced, surface cracks occur, and hot deformation resistance increases, making rolling difficult. On the other hand, when the heating temperature exceeds the β transformation point +100°C, the surface of the titanium alloy ingot is significantly oxidized, causing increased scale loss and surface flaws during rolling. Processing in the above temperature range requires a total reduction rate of 30% or more, and if it is less than 30%, the accumulated strain energy will not be sufficient and a sufficient effect of homogenizing the structure in the subsequent hot rolling process will not be obtained. The slab manufactured under such processing conditions is cooled, reheated, and hot rolled to manufacture a titanium alloy plate. Next, the hot rolling conditions of the present invention are to heat the slab manufactured under the above processing conditions to a temperature in the α+β2 phase region, apply a reduction with a total reduction rate of 30% or more at a temperature in the α+β2 phase region, and then hot roll the slab to a predetermined size. Roll into rolled plate. A batch furnace or a continuous furnace is used to heat the titanium alloy slab. The reason why the heating temperature was defined as the temperature in the α+β2 phase region is as follows. In other words, in the present invention, during the heating process of the slab at a temperature in the α+β2 phase region, recrystallization progresses based on the strain energy in the material stored in the slab manufacturing process, and the structure becomes uniform. When heating to a high temperature in the β region, cooling from the β region temperature results in gradual cooling to a temperature near the βα+β transformation point, and network-like coarse grain boundary α crystals precipitate at the prior β grain boundaries, which is the result of the present invention. This is because the effect of uniformizing the structure of the slab is lost. Furthermore, if the total reduction ratio of processing at a temperature in the α+β2 phase region is less than 30%, the effect of homogenizing the structure that is expected in the heat treatment process of a rolled plate cannot be obtained. [Example] Ti-6%Al-4%V alloy ingot (diameter
550mm) was heated to 1050℃ and subjected to blooming rolling.
Slabs with a thickness of mm were created. Slabs cut from this slab with thicknesses ranging from 120 mm to 45 mm are then hot-rolled in a temperature range of 950 to 800°C to form rolled plates with a thickness of 36 mm. →WQ＋538℃×6hr→A.
C.) The mechanical properties of the heat-treated material (STA material) were investigated. The results are shown in Table 2 together with the manufacturing conditions. The mechanical properties of rolled and heat-treated materials were investigated by taking specimens with a parallel part of 8.75 mmφ and G.L 35 mm from the center of the plate thickness in the l direction.
The test was conducted using a test piece measuring mm ^l × 100 mm ^w × 12.5 mm ^t . moreover,
Macroscopic non-uniformity is a problem in the structure of α+β type titanium alloys, so the uniformity of the structure is the average grain size of α crystals (average of 30 grains) in the LZ plane for STA materials.
was measured at 100 locations on the heat-treated material, and evaluated by comparing the standard deviation of this average grain size under each rolling condition.

【table】

【table】

〔Effect of the invention〕

According to the present invention described above, it is possible to appropriately manufacture a titanium alloy plate having a uniform structure, excellent mechanical properties such as elongation, and free from surface cracks, which is an excellent industrial effect.

[Brief explanation of the drawing]

Figures 1A and 1B are enlarged microscopic photographs of the structure of the No. 1 material in Table 2, with A showing the as-rolled material and B showing the heat-treated material. Figure 2 A and B are in Table 2
This is an enlarged microscopic photograph of the structure of material No. 6, in which A shows the as-rolled material and B shows the heat-treated material.

Claims (1)

[Claims] 1. A method for producing a titanium alloy plate, which comprises forming a slab by forging or rolling an α+β type titanium alloy ingot at a temperature in the α+β2 phase region at a total reduction rate of 30% or more. 2. After forging or rolling an α+β type titanium alloy ingot at a temperature in the α+β2 phase region with a total reduction rate of 30% or more, after reheating the slab to a temperature in the α+β2 phase region,
A method for producing a titanium alloy sheet, characterized by hot rolling at a total reduction rate of 30% or more. 3. The method for producing a titanium alloy plate according to claim 2, characterized in that the hot rolled plate is further heat treated.